fixed int/unsigned int parameter incompatibility

modules/tm/t_msgbuilder.c

@@ -172,7 +172,7 @@ char *build_uac_request(  str msg_type, str dst, str from,
 		struct cell *t, int *len)
 {
 	char *via;
-	int via_len;
+	unsigned int via_len;
 	char content_len[10];
 	int content_len_len;
 	char *buf;